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Food process engineering1
Microfiltration and Thermal Treatment for Extending the Shelf Life of Milk:
Factors affecting product quality and stability
Veronika Kaufmann1, Verena Schmidt2, Siegfried Scherer2 & Ulrich Kulozik1
1Chair for food process engineering and dairy technology; 2 Chair for microbial ecology
Food process engineering2
Factors affecting quality and shelf life of milk
ESL technology
= use of synergistic factorsfor efficient debacterization by
minimal processing impact on product properties
Thermal processing
High heattreatment
- 125-127°C → 2-4 s- 135°C → 0,5 s
directindirect
MicrofiltrationBactofugation
Non-thermal processing
Cross-flow
UTP-Concept
Gradientmembrane
Depthfiltration+
- Cream (and Retentate): 115-125°C → 3-4 s- Low bacteria milk: 72-75°C → 15-30 s
Thermal treatment
- Raw milk quality
- Process design and hygiene
- Filling and packaging
- Storage and distribution conditions
Food process engineering3
Conflicting targets of ESL-MF
Particle size [µm]0,01 0,1 1 10
Vol
ume
[%]
0
10
20
30
40
50
Casein(micelles)
Bacteria
Fat globules
Classicsterile
filtration
CurrentESL-MF
→ Objectives: efficient and selective debacterization of milk
Food process engineering4
Permeation of whey protein depending on pore diameter
Average pore diameter [µm]
Per
mea
tion
[%]
0
20
40
60
80
100a-lactalbumin xxxß-lactoglobulin
0,1 0,16 0,2 0,8 1,4
α-lactalbuminβ-lactoglobulin
MF:Skim milk ϑ = 50°C
100%)(CC
Permeationretentate
permeate ⋅=
Food process engineering5
Factors affecting filtration characteristics
Microorganisms/Particles
- Quantity- Size- Shape
Process- Temperature ϑ- Transmembrane pressure ΔpTM- Wall shear stress τw- Time t
Membrane- Material and surface structure- Effective filter area- Pore size and -distribution
Product- PH/IEP/ionic strength- Viscosity- Surface activity - Chem./physic. characteristics
Food process engineering6
Schematic diagramm of (UTP-)MF pilot plant
Plate heatexchanger
Tube heatexchangerMF (1,4 µm)
Feed tank
Plate heatexchanger
Tube heatexchangerMF (1,4 µm)
Feed tank
→ Operating conditions for ESL-MF: ΔpTM=0,2 barτW=150 Paϑ=55°C
Food process engineering7
Time [hours]
0 2 4 6 8 10 12
Per
mea
te fl
ux [l
m-2
h-1]
0
200
400
600
800
ϑ=55°CΔpTM=0,2 barτw=150 Pa
ϑ=10°CΔpTM=0,2 barτw=150 Pa
ϑ=55°CΔpTM=0,2 barτw=40 Pa
ϑ=55°CΔpTM=0,1 barτw=150 Pa
MF (1,4 µm):Skim milk
Influence of operating conditions on permeate fluxduring long-term filtrations
Food process engineering8
Permeation of protein and bacterial reductionduring long-term filtrations
Time [hours]
0 2 4 6 8 10 12
Pro
tein
per
mea
tion
[%]
98,0
98,5
99,0
99,5
100,0
log (N/N
0 )
0
1
2
3
4
0milkraw
permeate
NN log
NN
logreductiondecimalBacterial ==
MF (1,4 µm):Skim milk ϑ=55°CΔ pTM=0,2 barτw=150 Pa
100%)(CC
Permeationretentate
permeate ⋅=
Food process engineering9
Reduction of several microorganisms by MF* (I)
log (N/N0) [-]
- coccus:Ø = 1 - 3,5 µm
- gram-positive4,06 ± 0,26Micrococcus luteus
MorphologyGenus
- rods:1,5 - 3,0 x 0,5 - 1 µm
- gram-negative4,73 ± 0,18Citrobacter freundii
- rods:1,2 - 10 x 0,5 - 2 µm
- gram-positive4,37 ± 0,09Bacillus cereus
3,66 ± 0,23
- rods:1 - 2,2 x 0,6 - 0,8 µm
- gram-negativePseudoxanthomonas mex.
*MF (1,4 µm): Skim milk; ϑ=55°C; ΔpTM=0,2 bar; τw=150 Pa
Cell size
Food process engineering10
0,85 1,85 2,85 3,85
log
(N/N
0) [-
]
0
1
2
3
4
5
Reduction of several microorganisms by MF (II)
Bacilluscer.
Citro-bacter fr.
Pseudo-xanthomo-nas mex.
Micro-coccus lut.
MF (1,4 µm):Skim milkϑ=55°CΔpTM=0,2 barτW=150 Pa
5
4
3
2
1
log (N/N
heatedto 55°C ) [-]
0
gram-negative gram-positive
Cell size
→ Debacterization by MF = mechanical removal and thermal inactivation
Food process engineering11
...
References
Reference-databaseSpectrum
Unknown isolate
Comparison
Identification of microorganisms by FTIR-Spectroscopy
Identification
Food process engineering12
Comparison of flora compostion in skim, heated and MF-milk
3
3
20
21
10
43
Skim milkTBC=7,3*104 cfu/ml
other gram-positives
Bacillus ssp.
Coryneformes
Lactic acid bacteria
other gram-negatives
Pseudomonas ssp.
Genus
815
210
410
113
524
MF-milk*TBC=43 cfu/ml
Milk heated to 55°CTBC=3,1*104 cfu/ml
28
Quantity [%]
80
*MF (1,4 µm): ϑ=55°C; ΔpTM=0,2 bar; τw =150 Pa
Food process engineering13
Days of storage
0 5 10 15 20 25
Tota
l bac
teria
l cou
nt [c
fu/m
l]
1e+0
1e+1
1e+2
1e+3
1e+4
1e+5
1e+6
1e+7
Shelf life limit
Microbial growth during storage of MF- vs. MF+PAST-milk
→ MF decisive process step for debacterization of milk
104
105
106
107
103
102
101
0
MF
MF+PAST
stored at 10°CMF (1,4 µm)+ PAST (7373°°C/25 s)
→ Combination of MF+PAST essential for product safety and shelf life extension
rawskimmilk
off-flavour
Food process engineering14
Quantity [%]
Genus
10
30
58
2
-
-
TBC=18 cfu/ml
Day 0
5
12
83
-
-
-
TBC=80 cfu/ml
Day 7
other gram-positives
Bacillus ssp.
Coryneformes
Lactic acid bacteria
other gram-negatives
Pseudomonas ssp.
167
--
Day 21Day 14
7840
TBC=7·103 cfu/mlTBC=1,7·10² cfu/ml
53
-
-
6
-
-
Flora composition of MF+PAST*-milk during storage at 10°C
*MF (1,4 µm) + PAST (7373°°C/25 s)
Food process engineering15
Heat resistance of bacteria, spores and enzymes
12110,411Mesophilic spores (milk)
at ϑ [°C]z [°C]D [s]Species
1217,3 - 10,72,3Bacillus cereus (skim milk)
12110,425Thermophilic spores (milk)
79,36,90,50Enterobacter liquefaciens
Pseudomonas pseudomallei 0,52 9,3 73,3
Kessler, 1996
Lipase from15025100Pseudomonas
Pseudomonas flourescens
EnzymeProteinase from
660 34,5 130
Food process engineering16
Lipolysis and proteolysis during storage of MF+PAST-milk at 10°C
Days of storage
0 5 10 15 20 25 30
Free
fatty
aci
ds [µ
equi
v/m
l]
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
1,5
1,0
0,5
equiv. Tyr-Leu [µmol/m
l]
0,0
2,0
2,5
3,0
3,5→
Met
hod
byD
eeth
→Flourescam
in-Method
MF (1,4 µm)+ PAST (7373°°C/25 s)stored at 10°C
Food process engineering17
Days of storage
0 5 10 15 20 25 30
equi
v. T
yr-L
eu [µ
mol
/ml]
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
Influence of raw milk quality on proteolysis of MF+PAST-milk
off-flavour
MF (1,4 µm)+ PAST (7373°°C/25 s)stored at 10°C
c0=2,0 µmol/ml
c0 = 1,6 µmol/ml
Food process engineering18
Perspectives: Variation of process steps
Current processing: Alternative processing:
Raw milk
Cream
Retentate
Skim milk
Permeate
ESL milk
PasteurisationHigh HeatTreatment
Separation
Microfiltration
Raw milk
Cream
Retentate
Skim milk
Permeate
ESL milk
Pasteurisation
Separation
MicrofiltrationMicrofiltration
High HeatTreatment
Food process engineering19
Conclusions
- ESL-MF:
- Bacterial (decimal) reduction depends on morphology of microorganisms
- Reduction of bacteria = mechanical removal and thermal inactivation
- Decisive process step for debacterization of milk
- Combination of MF and thermal treatment:
- Ensures product safety and shelf life extension of milk
- Shelf life of MF+PAST-milk can be limited by enzymatical reactions
and depends on (microbial/enzymatical) raw milk quality
Acknowledgement:AiF/FEI → research project FV 15047 N